Access terminals, such as cell phones and wireless personal digital assistants (PDAs), are operable to communicate with radio access networks, such as cellular wireless networks. These access terminals and access networks typically communicate with each other over a radio frequency (RF) air interface according to a wireless protocol such as 1x Evolution Data Optimized (1x Ev-DO), perhaps in conformance with one or more industry specifications such as IS-856, Revision 0, IS-856, Revision A, and IS-856, Revision B. Other wireless protocols may be used as well, such as Code Division Multiple Access (CDMA), Global System for Mobile Communications (GSM), Time Division Multiple Access (TDMA), or some other wireless protocol.
Access networks typically provide services such as voice, text messaging (such as Short Message Service (SMS) messaging), and packet-data communication, among others. Access networks typically include a plurality of base stations, each of which forms one or more coverage areas, such as cells and sectors (that is, individual areas of a cell that allow the cell to carry more calls). When an access terminal is positioned in one of these coverage areas, it can communicate over the air interface with the base station (BS), and in turn over a signaling network or a transport network, or both. The signaling network may be a circuit-switched network, a packet-switched network or a combination of both. Similarly, the transport network may be a circuit-switched network, a packet-switched network or a combination of both.
Access terminals and access networks may conduct communication sessions (for example, voice calls and data sessions) over a pair of frequencies known as carriers, with a BS of an access network transmitting to an access terminal on one of the frequencies, and the access terminal transmitting to the BS on the other. This is known as frequency division duplex (FDD). A BS-to-access-terminal communication link is known as the forward-link, while an access-terminal-to-BS communication link is known as the reverse-link. The carriers may be segmented into various channels, such as pilot channels, sync channels, paging channels, control channels, traffic channels, access channels, and other channels.
Access terminals may be mobile such that the access terminals can be transported between different coverage areas formed by the same or different base stations. A given coverage area may reach a capacity for carrying out communications if too many access terminals are carrying out and/or are trying to carry out communications in the given coverage area.